Mistake #1: I know it's been said before buuuuut... being initially too close to uke:

As tori, you are bringing uke onto your back using your hands and your good body posture and positioning. Being too close to uke initially hampers tori's ability to get under uke and break their balance properly. When tori is too close to uke, the positive action of the strong kuzushi using the hands is greatly reduced.

Here, tori is too close to uke in this demonstration of seoi-nage (among other things gone wrong). With how close tori is to uke, it wouldn't matter how hard tori was pulling the kuzushi just would not be sufficient due to the lack of space between uke and tori. In this case, if uke was even a little heavier than tori, the throw would be very difficult.

In this demonstration, Matsuoka leaves a sufficient amount of space between himself and uke to:

1.) Maintain good posture (ie back to stomach, head up)
2.) Continue kuzushi, bringing uke's center of gravity over his own.
3.) Bring uke high onto his back.

In this video, Nomura's feet are very close to uke, which would seem to contradict the above, as he makes a very small rectangle (or even none at all). With the proper kuzushi and balance, however, he maintains the proper distance between himself and uke to do all that is necessary for the throw.

When he drops directly underneath uke, he is still continuously pulling, he still has good posture, (though he has to turn his head lest uke's face go directly into the mat [no score]) and he is able to bring uke high onto his back using his legs and hands in conjunction.

Mistake #2: Not loading uke properly:

Bringing uke high onto your back is essential for seoi nage. The harmony between hand action, body positioning, and leg strength is what makes this throw (or breaks it). For different people, that means different things. A person's leg strength is going to determine what kind of kuzushi is neccesary, and where their body positioning is going to be.

If your legs are weaker, you may have to adjust how you get your kuzushi, and where your body has to be positioned, many people adapt to this situation with so-called "drop" seoi-nage. Without leg strength, or a drop-knee seoi-nage the throw becomes very difficult, relying on good timing and perfect hand movement which is hard to cultivate (though you shouldn't stop trying).

If your legs are strong, you have far more options, as the strength can create opportunities, and salvage what would otherwise be failures.

There are not only two kinds of people who have strong legs and weak legs, the continuum of leg strengths creates the stylistic differences between different peoples' seoi-nage, but the basics of a good seoi-nage always remain the same.

Nomura can go low and spring back up using his strong legs. What if you're very tall and find it difficult to get low, or you lack the leg strength? The below version of seoi-nage, relies less on the legs, and emphasizes proper kuzushi, body positioning, and a twisting action that is unlike Nomura and Matsuoka. Look at how far away tori's legs initially are from uke's, especially compared to Nomura! This can enable to have to get as low as Nomura.

From tsukuri to kake (from entering into the throw to the throw itself) there are fewer blatant differences. Both have good body posture, and load uke high onto their back. They just go about it in different ways.

The picture below demonstrates how much foot placement and proper kuzushi matter. If you look at the first picture you'll see that tori (red) is nowhere near throwing uke, even as close to him as he is.

When you look at the second picture though, you see that though tori's feet are much further away than the first picture, that she (did I just blow your mind?) is much closer to throwing uke. Getting uke in position to be thrown by being underneath them is essential.

I'm sorry I'm not as l33t as UK is with this sort of thing, but I felt I could contribute a bit.

1. The triangle for Seoi Nage and in general (To clarify something for others, as I know you know this): The tip of the triangle is where you put your body in relation to uke, not just a foot. To be clear, when executing tai sabaki, tori moves his body into position at the top of the triangle (basics, there are exceptions).

A common error is to make tai sabaki (as part of the tsurikomi action) by stepping a foot first to a given location with the rest of the body following along. This disconnects your body action from your hands and thus does not transmit tori movement as efficiently to uke body.

2.) There are 2 primary methods of tai sabaki for Seoi Nage, both versions, in fact for most forward throws. 1 is back turning tai sabaki, where tori turns away from uke without ever moving towards him. The other is front turning tai sabaki, in which is as illustrated in Judoka_UK's post as the primary method. The third (basic) is a blend of the two and is probably most common with "experts" at seoi nage. If you have Nakanishi's book Masterclass series on Seoi Nage you can see it there. The pure back turning is most useful when uke is coming towards tori, the front turning when uke is moving away or static, although it is good for uke moving forward but is more difficult.

3.) It's the end of my shift, my relief is here, so I'm going home to drink beer, roast weenies, and shoot off illegal fireworks with my family to celebrate 4th of July.

If Judoka UK had been in charge back then, I'm sure we'd still be speaking with a funny accent and describing our weight in stones.

Ben

Falling for Judo since 1980

"You are wrong. Why? Because you move like a pregnant yak and talk like a spazzing 'I train UFC' noob." -DCS

"The best part of getting you worked up is your backpack full of irony and lies." -It Is Fake

"Banning BKR is like kicking a Quokka. It's foolishness of the first order." - Raycetpfl

I'm gonna very humbly add two tips that my coach has given me on Morote-Seoi-Nage (as it was his Tokeui-Waza when he was competing), and I've had some relative success with it in training.
Disclaimer: I'm a very lowly yellow belt, take everything I write at face value.

*Tips for a righty classic grip:

1. A split second before turning, give uke a pull, to open his gi - as in the other direction, from where you're gonna be going in a second. I don't know if this is just for off-balancing, more torque in your spin or plain to confuse uke. Hell for all I know it was just a thing he likes. But I've tried it and it helps my throw, so maybe it'll help you as well.

2. During the throw the sleeve hand should not be left behind you. make a fist when gripping and bring it to your chest (like a fist to chest Roman salute = "we who are about to die..."). Adding that motion when you spin helps tie up uke to you and gives you more control. Obviously the pull on the sleeve is more important, but this helps you if you're unsure what to do with lapel hand.

Those are my literal .02, hope they help somebody else as well.
Happy throwing.

2.) There are 2 primary methods of tai sabaki for Seoi Nage, both versions, in fact for most forward throws. 1 is back turning tai sabaki, where tori turns away from uke without ever moving towards him. The other is front turning tai sabaki, in which is as illustrated in Judoka_UK's post as the primary method. The third (basic) is a blend of the two and is probably most common with "experts" at seoi nage. If you have Nakanishi's book Masterclass series on Seoi Nage you can see it there. The pure back turning is most useful when uke is coming towards tori, the front turning when uke is moving away or static, although it is good for uke moving forward but is more difficult.

What Ben calls a back turn I call a forwards pivot and what Ben calls a front turn I call a backwards pivot, purely to confuse people reading this.

Classically the backwards pivot is how we teach throws statically, however, its actually quite problematic for beginners because having to reverse into someone as you're pulling them forward is actually quite a complex skill.

What I find better is teaching them to forwards pivot on the move. As that's much easier for people, because they get to preserve that forward momentum and have fewer spacing issues on entry. Its a little bit more complex for uke, because with a beginner you have to compensate for their errors.

Actually I was just thinking, wouldn't it be awesome if a very handsome, witty and eminently plus reppable Judo black belt had written an article explaining to beginners how to do a forward pivot for moving uchikomi practice. Wouldn't that be great...

Originally Posted by BKR

If Judoka UK had been in charge back then, I'm sure we'd still be speaking with a funny accent and describing our weight in stones.

Bugger that. I wouldn't have been messing around trying to keep a worthless and unprofitable colony. I'd have been in India making loadsa money turning myself into a Nabob.

Actually I was just thinking, wouldn't it be awesome if a very handsome, witty and eminently plus reppable Judo black belt had written an article explaining to beginners how to do a forward pivot for moving uchikomi practice. Wouldn't that be great...

Meh. What would really be awesome is if someone proselytized this training method to the masses. Otherwise as Johnny white belt I'm kind of stuffed. I can just see myself saying "excuse me sensei some alleged blackbelt on the internet who prefers to remain anonymous says your doing it wrnog. Can we please do uchi komi his way from now on?"

Not sure how well I can explain this, but i've been taught to grab high lapel instead of sleeve and then shoot my arm under to lock the shoulder or at least high above the elbow. Is this acceptable or am I just delaying my progress by getting too comfortable with this method?